L=wfbtlength(Ls,wt);
wfbtlength(Ls,wt) returns the length of a Wavelet system that is long enough to expand a signal of length Ls. Please see the help on wfbt for an explanation of the parameter wt.
If the returned length is longer than the signal length, the signal will be zero-padded by wfbt to length L.
In addition, the function accepts flags defining boundary extension technique as in wfbt. The returned length can be longer than the signal length only in case of 'per' (periodic extension).